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Application Scenarios
In a petrochemical plant’s emergency shutdown (ESD) system, two independent ABB SD822 power supplies are fed from separate UPS sources. Their outputs are connected to the SS822. The SS822’s output then powers the critical S800 I/O rack and AC 800M safety controller. If the primary UPS fails, causing Input A to drop, the SS822 detects the fault within milliseconds and continues drawing power solely from the healthy Input B. This zero-interruption switchover prevents a false trip of the ESD system, avoiding a multi-million dollar production shutdown.
Parameter
| Parameter | Specification |
|---|---|
| Model / Order No. | SS822 / 3BSC610042R1 |
| Product Type | Power Voting Unit (Redundant Power Manager) |
| Input Channels | 2 independent channels (A and B) |
| Input Voltage | 24 V DC (per channel) |
| Input Current | Max 20 A total (shared between inputs) |
| Output | 1 channel, 24 V DC, 20 A max continuous |
| Switching Logic | OR-ing (1oo2): Outputs voltage from the healthy input(s) |
| Monitoring | Per-input supervision (Undervoltage/Overvoltage detection) |
| Status Indication | LED indicators for each input status (Green/Red) |
| Mounting | DIN Rail (TS35, 35mm) |
| Width | 50 mm (compact footprint) |
| Operating Temp. | -25°C to +70°C (wide industrial range) |
| Compatible PSUs | ABB SD821, SD822, SD823 series |
| Status | Active / Critical Spare (Legacy & Current Systems) |
Technical Principles and Innovative Values
- Innovation Point 1: Solid-State “OR-ing” with Zero Voltage Drop: Unlike traditional redundant systems that use diodes (which cause a ~0.7V voltage drop and heat), the SS822 utilizes MOSFET-based OR-ing circuitry. This solid-state switching allows current to pass with minimal resistance, ensuring the full 24V reaches the load without significant loss. This is critical for maintaining the “hold-in” voltage of solenoid valves and contactors in safety systems over long cable runs.
- Innovation Point 2: Fault Detection and Predictive Maintenance: The module is not just a passive combiner; it actively supervises each input for under-voltage and over-voltage conditions. If a fault is detected, it can isolate the faulty path and, crucially, provide a remote alarm signal (via dry contacts or system bus). This allows maintenance teams to be alerted to a failing power supply beforethe backup source also fails, enabling proactive repair during planned outages rather than reactive emergency fixes.
- Innovation Point 3: High-Density Reliability: Designed for crowded control cabinets in power plants and offshore platforms, the SS822 packs 20A of managed power into a 50mm wide DIN rail module. Its fanless design relies on natural convection, eliminating a common mechanical failure point (the fan) and making it suitable for harsh, dusty environments where cooling fan blockages are a risk.
